The American Civil Liberties Union filed suit Tuesday on behalf of 23 Pennsylvania residents, including 10 couples, a widow and two children, naming Kane and the state's Republican Gov. Tom Corbett as defendants. Kane's move, announced to reporters at Philadelphia's National Constitution Center, places the burden of defending the law on the governor's general counsel. Corbett supports the prohibition on same-sex marriage, which passed the state legislature in 1996.

In an interview Kane--who endorsed the idea of gay marriage while running for her post last year--said she was obligated to drop the case “because I endorse equality and anti-discrimination laws.”

“If there is a law that I feel that does not conform with the Pennsylvania state constitution and the U.S. Constitution, then I ethically cannot do that as a lawyer,” she said.

Kane added that the Pennsylvania General Counsel, James D. Schultz, was fully capable of defending the governor, who was also named as a defendant in the ACLU lawsuit. “I’m not leaving them high and dry,” she said. “They have their own team.”

Thomas Peters, spokesman for the National Organization for Marriage, said Kane's refusal to defend the ban represented a sort of "pocket veto" of the law.

"This is just one more example of how the Supreme Court set a bad precedent [last month] in allowing elected officials to not represent the will of the people when they find it expedient," he said an in interview.

Proponents of California’s Proposition 8--the ballot initiative banning gay marriage in the state-- faced a similar problem after then Gov. Arnold Schwarzenegger (R-Calif.) and current governor Jerry Brown (D), who at the time served as California’s attorney general, declined to defend the proposition.

Last month the Supreme Court let stand a lower court ruling that the ban was unconstitutional, effectively reinstating the right to same-sex marriage in California. Part of the basis for the ruling was that backers of the initiative did not have the standing to appeal the lower court's decision to the nation's highest court.

Pennsylvania General Counsel James D. Schultz said in a statement he and his colleagues "are surprised that the Attorney General, contrary to her constitutional duty under the Commonwealth Attorneys Act, has decided not to defend a Pennsylvania statute lawfully enacted by the General Assembly, merely because of her personal beliefs."

"We have not received any formal notification of Attorney General Kane’s decision," Schultz added. "While we await that notification and accompanying legal justification, we will continue to review the lawsuit filed by the ACLU."

Kane framed her decision both in terms of her constitutional obligations and her commitment to Pennsylvania residents, saying that in a choice between defending the law and serving the public, "I choose you."

Mary Catherine Roper, a senior staff attorney for the ACLU of Pennsylvania, said she and others involved in the lawsuit were "celebrating" in the wake of Kane's announcement.

"To have the highest law enforcement official of the Commonwealth come out and say, 'I agree with you, this law is unjust, that’s huge for us,'" Roper said in a phone interview, her voice audibly emotional.

However the the state GOP chairman Rob Gleason released a statement calling it "unacceptable for Attorney General Kathleen Kane to put her personal politics ahead of her taxpayer-funded job by abdicating her responsibilities."

"She is blatantly politicizing the highest law enforcement office in our Commonwealth at the expense of a core responsibility of the Attorney General’s office," Gleason added. "Pennsylvanians are left with the question, if the Kathleen Kane’s political beliefs are the standard for law enforcement, what law will she ignore next?”

Roper said it was "too early to tell" how Kane's decision would affect the actual case, but said the 23 plaintiffs would continue to pursuit their suit against the state. "We’re ready to roll," she said.

Kane, the first woman and the first Democrat ever elected to the position of Pennsylvania state attorney general, said during last year's campaign she opposes a ban on same-sex marriage.

Juliet Eilperin is The Washington Post's White House bureau chief, covering domestic and foreign policy as well as the culture of 1600 Pennsylvania Avenue. She is the author of two books—one on sharks, and another on Congress, not to be confused with each other—and has worked for the Post since 1998.

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